Method for producing a connection interface in a filter element and device for producing the same

ABSTRACT

The invention relates to a method for producing a connection interface in a tubular filter element for filtering liquids, comprising a filter mat ( 10 ), the opposite ends ( 14 ) of said filter mat being interconnected in a connection position by means of a plane weld seam ( 28 ) which is provided with an impressed strip in the region of the free ends ( 14 ) of the filter mat. A region is provided between the impressed weld seam ( 30 ) formed in such a way and the beginning of the transition towards the tubular filter mats, in which a smooth weld seam ( 32 ) is applied without impression in a flat strip along the ends ( 14 ) of the filter mat. This enables the ends of the filter mat to be welded together in a strong and long-lasting manner, the impressed weld seam being simultaneously unloaded of any stress by means of the smooth weld seam. The invention also relates to a device for carrying out the method.

[0001] The invention relates to a method for producing a connection interface in a tubular filter element for filtration of fluids having a filter mat the opposite ends of which are connected to each other by a flat weld seam which is provided with an impressed strip in the area of the free ends of the filter mat. The invention also relates to a production device for application of the invention.

[0002] Filter elements produced in this manner are used for filtration of liquids such as ones in the form of hydraulic fluid or solutions of all kinds such as ones in the form of true suspensions, dispersions, emulsions, or colloidal solutions and have generally proved to be successful because of their compact structure and their large filter area. To make certain that the fluid flow is conducted only through the filter medium itself, in addition to the seal on the two ends, the connection interface of the two opposite ends of the filter mat in the form of end webs form one of the critical points which are to be closed so as to be leakproof.

[0003] Known filter elements such as are to be readily obtained through commercial channels may have a filter mat made up of various filter materials which are folded in zigzag fashion or are pleated mounted around a solid support tube provided with openings and which are enclosed in a fine-meshed wire screen which follows the fold contour of the filter mat as protection from external damage. In a part of the known processes for production of the known filter elements the connection interface in question of the filter mat ends, as well as the connection of the filter mat to the ends, are obtained by way of a bed of an adhesive, such as one in the form of an epoxy resin adhesive, but periods of waiting are needed until the adhesive becomes capable of bearing a load, depending on its gelling time, and may then be used after its setting period determined by the adhesive employed.

[0004] EP-B-0 001 407 discloses a process for production of a tubular corrugated filter element which is provided with at least one sheet of filter cloth whose edges forming a side connection are stacked and are connected to each other to form a side edge seal by means of a self-supporting groove-like strip. The strip, as an adhesively connecting strip, consists of a thermoplastic resin which encloses the edges of the filter sheet, the strip being adhesively joined to the filter sheet and the edges of the filter sheet being sealed together in an interlocking seal so as to be leakproof, as a result of which escape of an unfiltered fluid between the edges of the of filter sheet of the tubular filter element is prevented. The connecting strip involved forms a sort of U-shaped longitudinal clip which is welded to the ends of the filter mat by heating plates and accordingly after being subjected to heat and pressure.

[0005] Consequently, the adhesive connections described for the preceding disclosed process, as well as the accompanying production cost, are avoided. The free limbs of the disclosed strip-like connecting clip are designed to be flexible, so that these limbs may be moved apart when the ends of the filter mat are inserted so that the clamping pressure required may be applied to them for fastening. At the point of passage of the two free limbs of the longitudinal seam clip the latter forms a sort of stop against which the free ends of the filter mat ends come into contact and/or by which their movement in the direction of insertion into the clip is limited, so that the filter mat ends are flush with each other and assume the specified position required for production of the welded connection in the form of a smooth seam. It has been found, however, that, despite the steps provided for the purpose, the filter mat ends may be forced together during introduction of the configuration as described into a welding device, with the result that the quality of the weld seam to be applied may be appreciably lowered. Consequently, it is possible that the filter element may subsequently fail in the area of the welded seam points when in use. This is true in particular of filter elements subject to high stresses when the weld seam connection in question is separated, something which may result both in failure of the filter element and in failure of an entire hydraulic assembly in which the filter element in question has been installed.

[0006] DE-A-196 51 242 discloses the anvil of an ultrasonic sealing unit for sealing at least two fields of material consisting of backing material coated with plastic, with a sonotrode movable relative to the anvil, the seal surface on the front of the body of the anvil being contoured by means of raised and lowered areas. With the solution as disclosed it is not possible to seal or weld tubular filter elements and their filter materials by means of ultrasound and in the solution as disclosed a smooth weld seam is applied on the free end of the surface materials to be connected. This is favorable for application to milk cartons, since such cartons are designed to be opened easily by hand in the area of the smooth weld seam. Reliability in operation even under high load accordingly cannot be achieved with the solution disclosed.

[0007] WO 01/05483 A1 discloses a generic process for production of a connection interface in a tubular filter element having a pleated filter mat the opposite ends of which are fixed in position by way of a connecting strip which overlaps the ends at least in part, the connecting device consisting of a thermoplastic which is welded to the ends of the filter mat. The welding process is carried out without a welding filler and connects the clip to the ends of the filter mat in the fused state. In the welding process in question an impression is made in the connecting strip in the form of the plastic clip at least along one of its two sides in such a way that the filter mat ends are welded to each other in compressed form. Since the welding process can be carried out in an extremely short time simultaneously with introduction of the embossing, efficient production without use of additional epoxy resin adhesives or the like is possible, so that no holding or gelling times arise and the element may be used immediately or may immediately undergo additional processing.

[0008] Another result of the embossing is that the filter mat ends are welded together in compressed form so that an especially strong and lasting connection is obtained for the filter mat ends, even if these ends are subjected to very high fluid pressures during filtration. Since the filter mat ends are pulled apart beyond the embossed welding seam in the direction of the pleated elements of the filter mat because of the internal stress of the material, a wide gap occurs in this area, something which impairs the sealing efficiency and may be a factor if the embossed weld seam as produced is not entirely clean and is forced apart so that passages may be formed for undesirable escape of fluid. Introduction of material stresses into the embossed weld seam through the additionally widening gap occurs in the transitional area between pleating and embossed weld seam, so that the respective weld seam undergoes introduction of high punctate or linear forces to such an extent that failure may also occur, in particular if the filter element is subjected to alternating pressure stresses during operation.

[0009] On the basis of this state of the art the object of the invention is provision of a process for production of a tubular filter element and a device for production of such element which ensures connection of the filter mat ends as in the case of the solutions disclosed, but at the same time, in order to avoid use of adhesives, also result in reduction of the volume of material used in manufacturing and accordingly lower the production costs, and in addition yield reliably operating connection interfaces, even under the highest stresses. The object as thus formulated is attained by a process having the characteristics claimed in claim 1 and a device for application of the process as claimed in claim 10.

[0010] In that, as specified in the preamble of claim 1, there is provided between the embossed weld seam and the beginning of the area of transition to the tubular filter mat an area in which a smooth weld seam free of embossing is applied in a flat path along the filter mat ends, welding of the filter mat ends to each other in compressed form over the embossing is achieved as previously, so that an especially strong and durable connection of the filter mat ends is obtained even if such ends should be subjected to very high fluid pressures during filtration. At the same time, however, the embossed weld seam is relieved of stresses by way of the smooth weld seam, and in the event of any undesired penetration in the area of the embossed weld seam the smooth weld seam continues to be able itself to absorb the forces arising during operation of the filter element and to ensure leakproof connection of the filter element to the exterior. The average specialist in this field is surprised to learn that a better sealing result is obtained even by way of the smooth weld seam free of embossing than with the embossed weld seam used up to the present.

[0011] In addition to relief of pressure on the embossed weld seam by the smooth weld seam, however, the embossed weld seam is also advantageous for production of the smooth weld seam, since the free filter mat ends are precisely adjusted in relation to each other during the embossing process and so are connected to each other free of displacement. This feature also promotes improvement in the quality of the smooth weld seam, which is produced simultaneously with the embossed weld seam and accordingly is marked by very high production quality. Simultaneous application of smooth weld seam and embossed weld seam thus yields a synergistic effect, such that the two intrinsically different weld seam areas exert a favorable effect on the other weld seam area.

[0012] In that, in accordance with the specification of features in claim 10, the device claimed for the invention employs an ultrasonic welding device for production of the filter element in question, a connection process especially favorable with respect to energy is ensured for the filter mat ends.

[0013] In one preferred embodiment of the process claimed for the invention there is used for connection of the filter mat ends a connecting strip in the form of a clip which consists of a thermoplastic which holds the filter mat ends together during the welding process after the filter mat has been positioned on these ends. A connecting clip such as this is advantageous especially if the filter mat itself has only a small amount of plastic materials which may be joined together by thermal means. In addition, placing a connecting strip subsequently to be welded in position may be advantageous if the outermost filter mat layer consists of a metal support wire fabric.

[0014] In another preferred embodiment of the process claimed for the invention the embossing is in the form of rectangular, and in particular square, embossed elements which preferably are adapted to the lattice structure of the respective filter mat fabric. As a result, the respective embossing consisting of bonded plastic material may be introduced into the free spaces in the structure of the fabric so as to ensure a connection of especially great strength. If the fabric consists of a fabric material, the fabric material in question may be bonded directly to the embossed material of the respective embossing.

[0015] In one preferred embodiment of a device for application of the process as described in the foregoing use is made for the thermal welding process of an ultrasonic welding device having a sonotrode in the form of a strip and an anvil opposite it, the anvil at least being provided with an embossing device for application of the embossed weld seam and with an area free of embossing for application of the smooth weld seam. The device in question may thus be used in a single operating step for simultaneous application of the embossed weld seam and the smooth weld seam in the area of the filter mat ends.

[0016] The process claimed for the invention and the device for application of the process are described in what follows with reference to one form of embodiment as illustrated in the drawing, in which, in the form of diagrams not drawn to scale,

[0017]FIG. 1 presents a perspective view of the filter mat with the connecting clip, not welded;

[0018]FIG. 2 a section of the filter mat with connecting clip as shown in FIG. 1, not welded;

[0019]FIG. 3 a view of the filter element, partly as a front view, partly in cross-section;

[0020]FIG. 4 a perspective view of the essential components of the device for production of the welded connection;

[0021]FIGS. 5a,b a top view and a side view of a section of a part of the anvil shown in FIG. 4;

[0022]FIG. 6 the weld seam which may be produced expressly with the device shown in FIG. 4 by way of a smooth and an embossed weld seam in which the connecting clip is used.

[0023] A front view of the tubular filter element is presented in FIG. 3. It is used for filtration of fluids and has a filter mat 10 folded in zigzag form or pleated. Although not shown in detail, the filter mat 10 is made of multiple layers and may have the following laminate structure, for example, from the exterior inward:

[0024] 1. Metal wire fabric or plastic fabric or plastic screen with reticular structure,

[0025] 2. Polyester formed fabric,

[0026] 3. Glass fiber mat or meltblown formed fabric,

[0027] 4. Glass fiber mat or meltblown formed fabric,

[0028] 5. Paper fabric or polyester formed fabric,

[0029] 6. Composite special steel-polyester fabric,

[0030] 7. Metal wire fabric or plastic fabric or plastic screen with reticular structure.

[0031] To support the filter mat 10 there is provided in the interior of the filter element a metal support tube which is provided with fluid passages (not shown). The two opposite ends 14 of the filter mat 10 extend at an acute angle to each other and their length is kept somewhat shorter than the folds of the filter mat 10 mounted adjacent to them. Because of the layered materials used the tubular filter mat 10 is flexible and the pleated filter paths may be stacked, for example, as is illustrated by way of example in FIGS. 1 and 4. The support tube 12 consequently imparts a certain amount of stability to the filter mat 10 and defines its position in the subsequent filter element. A connecting device fastens the opposite ends 14 of the filter mat 10, the connecting device, as is shown in the figures, overlapping the ends 14 at least to some extent from the direction of their free ends. The connecting device is configured as a connecting strip 16 in the form of a clip 18 which, placed in position on the filter mat ends 14, holds these ends in position for a thermal welding process, the clip 18 being non-detachably connected to the filter mat ends 14 while in the melted state. The connecting device in the form of the connecting clip 18 preferably consists of a polyamide or polyester material which possesses good thermal welding properties.

[0032] For the sake of greater simplicity of presentation the individual layers of the filter mat 10 are shown in the illustrations as a laminated unit 20, the screen-like outermost plastic or metal wire fabric being designated as 22 in FIGS. 2 and 6.

[0033] As is to be seen in FIGS. 1 and 2 in particular, the plastic or connecting clip 18 is placed in position by its two free enclosing limbs 24 on the free limbs or free ends 14 of the filter mat 10 and as a result of its inherent elasticity the clamp 18 holds these ends 14 together. The two enclosing limbs 24 of the clip 18 are connected by way of a bow-shaped connecting piece 26, the connecting piece 26 forming a clearly defined contact area for the free ends 14 of the filter mat (10) because of the opposite enclosing limbs in this area. This makes certain that the two ends 14 end at more or less the same level and assume a clearly defined position relative to each other for the subsequently provided welding process still to be described. Because of the inherent elasticity of the clip 18 this possibility of clearly defined positioning is already provided in the area of the enclosing limbs 24 and not just in the bow-shaped contact base of the connecting piece 26. The plastic clip 18 is optimized in that the clear opening for insertion of the filter mat ends 14 are kept somewhat smaller than the width of the two stacked filter mats 14 so that, because of the elasticity behavior of the plastic of the clip 18, such clip is pressed into contact with the free filter mat ends 14. Production of the clip 18 may be made especially cost effective in that the clip, analogous to the filter mat 10, consists of stacked or pleated bows which are separated from each other and then form a longitudinal clip 18. In order not to impair the possibility of insertion of the filter mat ends 14 provision is also made such that, in the area of the clear ends of the two enclosing limbs 24, the clip 18 is provided with a bow-shaped insertion accessory extending outward.

[0034] In the welding process for production of the connection interface, with the filter mat ends 14 in the connected position illustrated, these ends are joined together by way of application of a flat weld seam; this weld seam, designated as a whole as 28, is provided in the area of the filter mat ends 14 with an embossed path and accordingly with an embossed weld seam 30, there being provided in contrast, between this embossed weld seam 30 and the beginning of the area of transition to the tubular filter mat 10, an area in which is introduced a smooth weld seam 32 free of embossing in a flat path along the filter mat ends 14. Consequently, the plastic clip 18 is thermally shaped by the welding process and then provided with embossing 34 (cf. FIG. 6) which corresponds more or less to the screenlike basic structure of the metal wire fabric 22, that is, the thermally shaped plastic material of the clip 18 enters the clear spaces inside the lattice structure of the plastic or metal wire fabric 22, so that an especially strong bonding is achieved, this bonding being additionally supported in that the laminate unit 20, which to some extent at least also contains plastic materials, is welded at the same time. Introduction of the embossing 34 is also accompanied by production of the smooth weld seam 32, which ensures, among other things, that the embossed weld seam 30, which is weakened at least to some extent in cross-section by the embossing 34, is kept free of harmful stresses resulting from changes in pressure and peak stresses. In the opposite direction the embossing 34 permits precise adjustment of the filter mat ends 14 during the welding process, so that the smooth paths come to lie cleanly one on the other in the area of the smooth weld seam and so a high-strength welded connection is achieved without the possibility of formation of a potential leakage point by any warping of the material of the path.

[0035] An ultrasonic welding process is used for welding the filter mat ends 14 to the connecting device, but other thermal welding processes may also be applied.

[0036] As is shown by FIG. 3 in particular, the linear relationships selected, in any event in the area of the connecting seam, are such that the connecting device, as viewed in the radial direction, ends along the outer radial circumference of the filter mat 10. Consequently, the filter mat ends 14 are embedded in the clip 18 when the latter is in the molten state, so that non-detachable, permanent bonding with the filter mat 10 or the filter element for later filtration is obtained. The embossing 34 in question may be made along one enclosing limb 24 or along both enclosing limbs 24. In addition, the respective connection interface may be produced by way of an embossed weld seam 30 and a smooth weld seam 32 also with the connecting device with the connecting strip 16 omitted. The connection in question is to be preferred especially if the filter mats 10 and accordingly the ends 14 as well have a highly weldable plastic component so that the welding process may be conducted without problems. In such a case it must be ensured for the equipment that the filter mat ends 14 will not be unintentionally displaced relative to each other during the welding process.

[0037]FIG. 4 illustrates the ultrasonic welding device 36 with which the thermal welding process may be carried out. The ultrasonic welding device has a sonotrode 38 in the form of a strip and an anvil 40 in the form of a strip. The anvil 40 of the ultrasonic welding device 36 is mounted so as to be more or less stationary, the sonotrode 38 being movable for a welding process in the direction indicated by the arrow in FIG. 4 from an initial position toward the welding deposit in the form of the straight bead clip 18 for a welding process. For the purpose of the welding process the filter mat 10 with its filter folds are placed together as indicated in FIG. 4 and, after the clip 18 has been placed in position, the filter mat ends 14 are welded to this clip. The welding process involved may be further facilitated by auxiliary handling measures. It is also possible, however, to introduce the filter mat 10 into the welding device 36 by hand.

[0038] After the welding process has been completed, the sonotrode 34 is removed and the weld seam is formed as shown in FIG. 6. The filter mat 10 may be converted to a tubular configuration and assembled on the support tube 12 as a further addition to the complete filter element.

[0039] The welding process effects sealing of the bevel edges to prevent fiber migration, so that, for example, glass fibers of the filter medium are effectively retained in the filter mat 10. The clip 18 is dimensioned with respect to the amount of plastic required so that the connecting seam may be produced in any event without welding filler. The filter mat 10 claimed for the invention and the device 36 for producing this filter mat make possible an efficient production process without use of a connecting adhesive such as an epoxy resin adhesive, so that there is no period of waiting for the adhesive to set and the filter mat 10 or the filter element may immediately be put to further use. Dispensing with the adhesives regularly containing solvents also has a favorable effect on the environment.

[0040]FIGS. 5a and 5 b present a top view and a side view of a section along the top of the anvil 40. As is thus to be seen in FIGS. 5a and 5 b, the embossing 34 is obtained with individual elements 44 square in cross-section. FIG. 5b, which represents a cross-section along line I-I in FIG. 5a, makes it clear that the respective individual elements 44 are roof-shaped in cross-section in their areas of transition, the flat roof elements 46 being positioned in a plane with the top of the fusion welding sheeting 48 producing the top of the smooth weld seam 32. The fusion weld seam in question 48 is approximately the same in width as the total width of the individual roof elements 46 of the individual elements 44, which are integrated into the top 42 of the anvil 40 in two parallel rows. The individual elements 44 are provided with corresponding drafts relative to their roof elements 46 in order to be able to ensure a good ejection process. A mold release bevel 50 such as this is also provided in the area of transition between the individual elements 44 and the fusion welding sheeting 48.

[0041] The embossed weld seam 30 which may be produced in this way by means of the anvil 40 and the smooth weld seam 32 complement each other very logically and make possible production of reliable high-strength connection in the area of the filter mat ends of filter elements. 

1. A method for producing a connection interface in a tubular filter element for filtration of fluids, having a filter mat (10) the opposite ends (14) of which are interconnected at a connection point by way of a flat weld seam (28) and are provided in the area of the free filter mat ends (14) with an embossed strip, characterized in that there is provided between the embossed weld seam (30) thus formed and the beginning of the area of transition to the tubular filter mat ends an area in which a smooth weld seam (40) free of embossing is applied in a flat strip along the filter mat ends (14).
 2. The process as claimed in claim 1, wherein the weld seam (28) in the form of the embossed strip (30) and the strip (32) free of embossing are applied simultaneously.
 3. The process as claimed in claim 1 or 2, wherein, for the purpose of connecting the filter mat ends (14), a connecting strip (16) in the form of a clip (18) is introduced, such strip (18) consisting of a thermoplastic material and, after being placed in position on the filter mat ends (14), holding such ends together during the welding process.
 4. The process as claimed in one of claims 1 to 3, wherein a plastic fabric (22) is employed for the filter mat (10) at least on the outer circumference or wherein the filter mat (10) itself consists at least in part of thermoplastic materials.
 5. The process as claimed in one of claims 1 to 4, wherein the embossing (34) consists of rectangular, in particular square, embossing elements (44) which preferably are adapted to the screen structure of the respective filter mat fabric.
 6. The process as claimed in one of claims 1 to 5, wherein the tubular filter mat (10) is provided both with pleating and with a multilayer structure and wherein at least a polyester formed fabric and/or a glass fiber layer and/or a meltblown formed fabric and/or a composite special steel and polyester fabric or a plastic fabric and/or a metal wire fabric (22) are/is provided as layers.
 7. The process as claimed in one of claims 3 to 6, wherein a polyamide or polyester material is used as material for the connecting strip (16).
 8. The process as claimed in one of claims 1 to 7, wherein welding of the filter mat ends (14) is effected without a welding filler and without a connecting strip (16), by way of an ultrasonic welding process.
 9. The process as claimed in claim 3 to 8, wherein the connecting strip (16) is applied in the radial direction of the filter mat (10), along the outer circumference of such filter mat (10).
 10. A device for application of the process as claimed in one of claims 1 to 9, characterized in that there is used for the thermal welding process an ultrasonic welding device (36) having a sonotrode (38) in the form of a strip and an opposite anvil (40) and wherein the anvil (40) is provided with embossed elements (44) for application of the embossed weld seam (30) and with fusion welding sheeting (48) free of embossing for application of the smooth weld seam (32). 